Semiconductor integrated circuit chemical-mechanical planarizing slurries are utilized by the semiconductor industry in the manufacture of integrated circuit devices. Various semiconductor integrated circuit layers are stacked on top of a semiconductor substrate. The stacked layers are deposited and formed on the semiconductor substrate so that electrical connections can be made to the devices incorporated in the semiconductor substrate wafer and the devices can perform their intended functions (such as computations and computer processing). Chemical-mechanical planarization utilized in the stacking of such layers and formation of such electrical connections to remove deposited materials and provide flat planar surfaces.
Application of colloidal suspensions for polishing planarizing advanced materials has become an exceedingly critical aspect of final part formation for the semiconductor integrated circuit microelectronics industries. Silica and alumina colloids are formed through various techniques and typically require expensive precursor materials in order to ensure the highest purity products. Solutions are stabilized with buffer systems to pH and solids loading values that result in optimal semiconductor workpiece surface finish attainment. Particle size distribution can be adjusted to control the final surface finish as well as the ability to clean residue abrasive particles from workpiece surfaces after processing. The present invention describes the application of colloidal silica soot produced as a byproduct of chemical vapor deposition processing of glasses in the semiconductor integrated circuit finishing industry, specifically for application to silicon wafers, oxide coating on such wafers, conductive metals used in microelectronic devices (e.g., aluminum, copper, tantalum, tungsten, etc.), and ceramics used in microelectronics (e.g., silicon nitride and silicon carbide).
The abrasive particles of a CMP slurry effect the slurry chemistry and its use. The slurry solution must be adjusted to a pH that will allow for attainment of the best surface finish and the solution must be stabilized from agglomeration and pH shifts during storage. For conventional colloidal silica abrasives designed for microelectronic applications, buffers solutions using mixtures of various bases and salts are incorporated for stabilization anywhere between pH 5-12. Most common for colloidal silica solutions stabilized for single-crystal silicon polishing is a buffer adjustment to pH 10-11. For the Soot of the invention, a likewise adjustment can be made using a potassium-based buffer solution.
With regards to polishing of interconnecting metals in microelectronic integrated circuit devices (e.g., aluminum, copper, tantalum, tungsten, etc.) the soot materials offer advantages including (1) relatively large particle size (>0.25 μm) with spherical morphology and (2) added stabilization of TiO2—SiO2 over SiO2. The inventive soot materials demonstrate four preferred points in specific application to the chemomechanical polishing (planarization) of microelectronic materials such as copper, aluminum, tungsten, and silicon as well as related carbides and nitrides:
First, the Ti doped soot shows significantly improved stability at low pH (<pH 5) as compared to the pure silica soot. This provides the doped soot with better dispersion properties and beneficial performance when being applied as a polishing compound at pH <5.
Second, the pure undoped fused silica soot is shown to be of greater resistance to dissolution at high pH (pH >5), suggesting that the soot would perform in a superior manner that the Ti doped soot for microelectronic applications in this pH range.
Third, the decreased surface area of the inventive soots (10-20 m2/gram) as compared to competing silica particle materials (100-400 m2/gram) such as fumed silica suggests that these soot particles can be dispersed in solution using less dispersion aids, thus eliminating sources of contamination or unwanted levels of dispersion aids used.
Fourth, the spherical nature and particle sizes of the inventive soot materials suggest that the mechanical performance of the soot materials used as abrasive particles would not scratch the surface being polished.